The present invention generally relates to manufacturing processes and equipment using masks and masking structures and, more particularly, to the selection and storage of masks and mask structures in an entire semiconductor processing system.
A conventional semiconductor fabrication plant typically includes multiple fabrication areas or bays interconnected by a path, such as a conveyor belt. Each bay generally includes the requisite fabrication tools (interconnected by a subpath) to process semiconductor wafers for a particular purpose, such as photolithography, chemical-mechanical polishing, or chemical vapor deposition. Material stockers or stocking tools generally are located about the plant and store semiconductor wafers waiting to be processed. The wafers are typically stored in containers, such as cassettes, each of which can hold up to 25 wafers. The cassettes are then stored in carriers that facilitate movement throughout the plant.
The semiconductor fabrication plant, including the bays, material stockers and the interconnecting path, typically operates under control of a distributed computer system running a factory management program. In this environment, the automated material handling system (AMHS) conceptually includes the cassettes, the transportation system (e.g., paths) and control system (e.g., the distributed computer system). The AMHS also typically include empty carriers management system as well as a separate test wafer management system.
A wafer is subjected to a photolithography process of some type and usually involves applying a layer of photoresist material, such as silicon dioxide, over the surface of a wafer using a coating machine. The wafer is then moved to an exposure tool, such as a photolithography stepper, that exposes the photoresist layer to a patterned light source. The light source is patterned using a mask structure or a reticle. The reticle contains clear and opaque features that generally define the pattern to be created in the photoresist layer. The exposed photoresist is then developed and regions of the photoresist are dissolved leaving a pattern on the photoresist layer. The exposed portions of the underlying wafer are then subjected to further processing.
Depending on the type of IC device being manufactured, the wafer may be subjected to the photolithography process several times as layers are formed successively over prior layers to ultimately form the semiconductor device. To perform the various photolithography processes, a semiconductor plant has a photolithography processing area that occupies a substantial amount of floor space and involves a high level of capital investment to maintain. The photolithography area usually includes a number of steppers that utilize an entire cataloged library of reticles. The number of reticles that need to be readily available can easily exceed one thousand, due to the number of different products that can be manufactured in one facility, with each reticle having a replacement cost of about $15 K. The reticles are usually stored in a reticle storage system, centrally located within the photolithography area, and are cataloged by reticle identification number. The reticle is then transported via a conveyor system to the particular stepper in need of a certain reticle. One of the problems with managing reticles is that they are very delicate structures and can be damaged easily by excessive handling. They also need to be routinely inspected to ensure that they are still viable for use in making the intended product.
Cycle times for the photolithography processing areas have increased due to the wafer processing system""s limited resources that are available to manage all of the options available on the processing line. One of the problems with the current reticle management systems is the substantial manual intervention required in managing the finite number of reticles in inventory, the limited number of the duplicate reticles available and the finite number of pods that move the reticles around the photolithography area. In addition, operators on the line must manually coordinate any changes to the reticle flow or storage plan. This approach has led to delays in the wafer processing system and has caused inefficiencies in manufacturing. Further, midstream changes in production are relatively difficult and slow to respond to due to the decentralized management of reticles and reticle storage locations.
The present invention is directed to addressing the above and other needs in connection with improving efficiencies of reticle stocking and sorting processes.
According to one aspect of the invention, it has been discovered that allowing on-demand reticle selection reduces cycle time and increases flexibility on the manufacturing line. It has also been discovered that reducing the amount of handling of reticles and determining early the level of degradation that a reticle is exhibiting reduces the overall capital investment in this area. An integrated reticle sorter/stocker device, according to the present invention, reduces the handling of reticles and aids in the real time evaluation of the viability of reticles for wafer processing.
According to another aspect of the invention, a mask stocking and sorting management system is used in a manufacturing facility having a material handling system that presents a mask to a photolithography process area. The system includes an arrangement of pods, each of the pods including at least one mask, and a host system adapted to rearrange the pods at a mask storage location as a function of a mask identification code and an externally provided directive indicating a masking sequence change. In another related embodiment at least one mask sorting apparatus can be coupled to the mask storage system and to the host system to provide more flexibility in the overall mask management system. An important advantage is that the host system reduces the delivery time of a mask to the photolithography area and reduces the number of buffer pods used in the material handling.
According to another aspect of the present invention, a method of stocking and sorting masks is used in a manufacturing facility having a material handling system for presenting a mask to a photolithography process area. An arrangement of pods is provided with each of the pods including at least one mask. The pods are then rearranged at a mask storage location as a function of a mask identification code and an externally provided directive indicating a masking sequence change. An important advantage is that the method reduces the delivery time of a mask to the photolithography area and reduces the number of buffer pods used in the material handling.
In yet another aspect of the present invention, a method of stocking and sorting masks in a manufacturing process involves a photolithography process area and a material handling system. The method includes conducting a status check of all of the masks in the manufacturing process and then preparing a mix of masks within a mask storage system to be transported to the photolithography area via the material handling system. A host system is polled to determine the existence of an instruction change that can change the flow of masks in the manufacturing process. The masks are then used in the photolithography process, are returned to the storage location and the status of the masks are communicated to the host system.
In yet another aspect of the invention, an apparatus for sorting and stocking a plurality of masks for use in a wafer processing system includes a scanning device that identifies a mask identification code located on each mask and scans the dimensions of each mask. A sorting device sorts the masks within a stored location. A computer arrangement is adapted to control the scanning device and the sorting device and to record data retrieved therefrom, the computer arrangement is adapted to analyze the mask data in determining a level of mask degradation for each mask before a mask selection is made.
In yet another aspect of the invention, a system for sorting and stocking masks for use in a wafer processing facility includes a mask data set generator that includes information on a mask identification code for each mask and includes a dimension data for each mask. A mask degradation analyzer adapted to conduct degradation analysis on each mask that includes a comparison of the mask data set to a mask baseline dimension so as to generate degradation data for each mask. A computer arrangement is used to record and analyze the degradation data and the mask data set before making a mask selection. A mask-sorting device is adapted to rearranging the masks at a mask storage location in response a mask selection command from the computer arrangement based on the data analysis.
In yet another aspect of the invention, a method of sorting and stocking masks used in a wafer processing facility includes providing a mask data set that includes information on a mask identification code for each mask and a dimension data for each mask. A computer arrangement is used to conduct a degradation analysis on each mask that includes comparing the mask data with a baseline dimension of each mask so as to generate degradation data for each mask. The computer arrangement records and analyzes the degradation data and the mask data set before a mask selection is made. The masks are then rearranged at a mask storage location in response to a command from the computer arrangement based on the data analysis.
In yet another aspect of the present invention, a method of sorting and stocking masks in a wafer processing facility, having a photolithography processing area, includes conducting a status check of masks in the facility and generating a mask data set. A mix of masks is prepared within a mask storage system and the mix is then presented to the photolithography area. A host system is polled to determine existence of an instruction that changes the flow of masks in the photolithography processing area. A degradation analysis is conducted on the masks so as to generate degradation data for each mask and then a computer arrangement is used to record and analyze the degradation data and the mask data set. The masks are rearranged at a mask storage location in response to a command from the computer arrangement based on analysis. The mask status is then communicated to the host system.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures in the detailed description that follow more particularly exemplify these embodiments.